Forgot to follow up: using exact matches works for me, without spaces, even if they contain "Unknown", e.g.

profile home {
    output "Unknown Q27G2G4 0x000064B2" position -2179,0 scale 1.175 mode 2560x1440@143.9Hz
    output "Unknown MSI MAG161V AA1H010800597" position 0,360 scale 1.4
}

So yes, this was a bug in kanshi which got fixed.

Can you clarify what you mean by this: was it a bug that partial names were matching before, or is it a bug that only exact names are matching? I'm happy switching to exact names in the config, just making sure.

My config profile no longer works with version 1.3, resulting in a "no profile matched" message. The profile, which works with version 1.2.0-4 from the Arch repos is:

profile home {
    output "Unknown Q27G2G4" position -2179,0 scale 1.175 mode 2560x1440@143.9Hz
    output "MSI MAG161V" position 0,360 scale 1.4
}

From swaymsg -t 'get_outputs' I get:

Output HDMI-A-4 'Unknown MSI MAG161V AA1H010800597' (focused)
  Current mode: 1920x1080 @ 60.000 Hz
  Position: 0,0
  Scale factor: 1.000000
  Scale filter: nearest
  Subpixel hinting: unknown
  Transform: normal
  Workspace: 1
  Max render time: off
  Adaptive sync: disabled
  Available modes:
    1920x1080 @ 60.000 Hz
    1920x1080 @ 60.000 Hz
    1920x1080 @ 59.940 Hz
    1920x1080 @ 50.000 Hz
    1920x1080 @ 50.000 Hz
    1680x1050 @ 60.000 Hz
    1280x1024 @ 60.020 Hz
    1440x900 @ 59.901 Hz
    1366x768 @ 59.949 Hz
    1280x800 @ 59.910 Hz
    1280x720 @ 60.000 Hz
    1280x720 @ 59.940 Hz
    1280x720 @ 50.000 Hz
    1024x768 @ 60.004 Hz
    800x600 @ 60.317 Hz
    720x576 @ 50.000 Hz
    720x576 @ 50.000 Hz
    720x480 @ 60.000 Hz
    720x480 @ 60.000 Hz
    720x480 @ 59.940 Hz
    720x480 @ 59.940 Hz
    640x480 @ 60.000 Hz
    640x480 @ 59.940 Hz
    640x480 @ 59.940 Hz

Output HDMI-A-5 'Unknown Q27G2G4 0x000064B2'
  Current mode: 2560x1440 @ 59.951 Hz
  Position: 1920,0
  Scale factor: 1.000000
  Scale filter: nearest
  Subpixel hinting: unknown
  Transform: normal
  Workspace: 2
  Max render time: off
  Adaptive sync: disabled
  Available modes:
    2560x1440 @ 59.951 Hz
    2560x1440 @ 143.912 Hz
    2560x1440 @ 119.998 Hz
    2560x1440 @ 99.946 Hz
    1920x1200 @ 59.951 Hz
    1920x1080 @ 120.000 Hz
    1920x1080 @ 119.880 Hz
    1920x1080 @ 60.000 Hz
    1920x1080 @ 60.000 Hz
    1920x1080 @ 59.940 Hz
    1920x1080 @ 50.000 Hz
    1600x1200 @ 59.951 Hz
    1280x1440 @ 59.913 Hz
    1680x1050 @ 59.951 Hz
    1280x1024 @ 75.025 Hz
    1280x1024 @ 60.020 Hz
    1440x900 @ 59.951 Hz
    1280x800 @ 59.951 Hz
    1280x720 @ 60.000 Hz
    1280x720 @ 59.940 Hz
    1280x720 @ 50.000 Hz
    1024x768 @ 119.989 Hz
    1024x768 @ 75.029 Hz
    1024x768 @ 70.069 Hz
    1024x768 @ 60.004 Hz
    832x624 @ 74.551 Hz
    800x600 @ 119.972 Hz
    800x600 @ 75.000 Hz
    800x600 @ 72.188 Hz
    800x600 @ 60.317 Hz
    800x600 @ 56.250 Hz
    720x576 @ 50.000 Hz
    720x576 @ 50.000 Hz
    720x480 @ 60.000 Hz
    720x480 @ 60.000 Hz
    720x480 @ 59.940 Hz
    720x480 @ 59.940 Hz
    640x480 @ 75.000 Hz
    640x480 @ 72.809 Hz
    640x480 @ 66.667 Hz
    640x480 @ 60.000 Hz
    640x480 @ 59.940 Hz
    640x480 @ 59.940 Hz
    720x400 @ 70.082 Hz

I tried various small changes like deleting the "Unknown" part or adding it before the MSI monitor code, or deleting the 144Hz setting, or changing to single quotes, but nothing simple like this seemed to have any effect.

For anyone else landing here, the upstream issue is tracked at: https://github.com/gdamore/tcell/issues/356